Boring deep holes

[Mark P.Participant @markp]

Hello all,I am embarking on a project which entails boring 2 parallel holes in an aluminium block.Both are 150mm deep,one is 20mm dia and the other is 12.5 mm dia. The 20mm one has a closed end while the 12.5mm one is open ended,I’m planning to ream this one,it’s the 20mm one which is the problem.Would I be best off making a substantial boring bar or drilling and buying a 20mm reamer to hold in the lathe chuck?

Any tips/ideas gratefully recieved. Pailo.

[Mark P.Participant @markp]

[John HaineParticipant @johnhaine32865]

I’d make a boring bar. I’ve made a few of these, they are very easy, using both HSS and carbide inserts. HSS is easier, just drill and ream a hole for the bit and drill and thread another hole at right-angles for the locking screw. For a flat-bottomed hole the toolbit will have to be at 45 degrees so it slightly projects from the bar, and it may be difficult to get the hole completely flat-bottomed. I have found big reamers to be a bit problematic to handle, and you would anyway need a machine reamer to get a blind hole parallel.

[Ramon WilsonParticipant @ramonwilson3]

Hi Pailo

 

I would agree with John but bearing in mind the following proviso – boring over that length may – ‘may’ – produce a slightly tapered bore regardless of how many cuts at the same setting are taken. Whilst reaming will ensure the size it won’t necessarily give a good finish (if that’s an important requirement) especially as it’s a long hole to get coolant/cutting fluid down the flutes and it will not of course give a square corner if that is required.

 

Make the bar as large as you can for the finishing cuts – that is go for maximum rigidity Sharpen the bit for that last .25mm on diameter and keep it lubricated to prevent build up on the tool tip. You may need to use a thinner bar to face across the bottom after the bore is sized.

 

Hope that helps a bit more – Ramon

 

 

[TerrydParticipant @terryd72465]

Hi Pailo,

 

You could try a D bit made from 20mm silver steel (drill rod) they are simple to make and with care will produce a flat bottomed hole and can produce a better finish than a reamer (cheaper too). Using a milling machine to create the flat and end shape it would take you around 25 mins to produce one including hardening and tempering.

 

They are not considered enough these days of buy it all ‘sophisticated’ tooling. Here is a quote about the D bit from an early machinists manual:

 

“This is a true cutting tool, and will not only enlarge holes, but will initiate and bore holes through solid metal. There is hardly a limit to the capability of this most perfect tool. It will bore to almost any diameter and length with extreme accuracy, provided it is sufficiently lubricated.” (my emphasis)

 

See here for a description of making one, it is not too clear but there is a section in G H Thomas’ book on making these which produces very good drills.

 

 

Regards

 

Terry

[mickParticipant @mick65121]

As long as the work is firmly held down and you have suitable drills, then double drilling might be a better option. Drill a pilot hole with the V point to depth, follow up with a 3/4” leaving 1mm to come out. Drill down with the 20mm drill till the V point is a depth. Then grind of the drill point to make a flat bottomed drill, which can then be used to clear out the V section at the bottom of the hole. The hole should be dead size and parallel

If you encounter juddering when following with a larger drill, try using a piece of worn emery tape folded double and placed on the top of the hole. The tape will fill the flutes and stop the juddering and cut a clean hole.

[Keith LongParticipant @keithlong89920]

Hi Pailo

It might be a silly question, but can you make to 20mm hole a through hole, finish it as required and then plug it from the back. Might be easier.

Keith

[John OlsenParticipant @johnolsen79199]

I’d agree with Terry on the D bit. They are not the fastest cutting device, but do leave a very good finish including a square end. If you don’t happen to have a chunk of silver steel that size, you could probably get away with making one from mild steel and case hardening, provided you don’t want too many holes.

 

I’ve also made a couple of cutters, for when I didn’t have the right size drill for half and 3/4 BSP. (Still don’t.) They are a hollow tube shape, with teeth filed on the end, and then hardened and tempered. (from Silver steel.) Note that no dividing gear is used, the teeth are filed by eye with a three corner file to try to maintain the same cutting height. The hole is drilled undersize and then the cutter is used to take it out to the tapping size. These work well for short holes, as they tend to be for BSP, so I don’t know how good they would be for enlarging longer holes. Since there is no provision for chips to escape, other than finding their way to the centre hole, it pays to back out often.

 

regards

John

[Mark P.Participant @markp]

Thanks for the replies,I think that I will go for the D bit idea as I have some 20mm Silwer steel (though I can’t for the life of me where it came from!)

Regards Pailo.

[Ian S CParticipant @iansc]

You could also make a D bit out of mild steel by brazing a piece of HSS on the culling edge. A short length of silver steel could be attached to the end of a mild steel bar that could be smaller in dia than the working part of the drill. Ian S C

[TerrydParticipant @terryd72465]

Hi Pailo,

 

If you need the specification I can copy the G H Thomas article for you.

 

Regards

 

Terry

[Mark P.Participant @markp]

Hi Terry would be good if you could copy the G H Thomas article please.

Regards Pailo.

[TerrydParticipant @terryd72465]

Hi Pailo,

 

Please send me a PM with your email address and I will post it off to you,

 

Best regards

 

Terry

[mgjParticipant @mgj]

If you are going to go the d bit route…., and I must admit I wouldn’t. I’d just single point bore it. in a soft material like ali I think there would be very little problem with a decent stout boring bar.

 

Why not a d bit. Well you need a fair bit of torque to drive a d bit of that dia, and all needs to be pretty dead straiht. or the sides will jam on a long hole like that. Equally the ali is going to get a bit warm, and with a d bit you have no clearance – and you could find, with ali’s propensity to pick up, with a lovely bit jammed pretty solid. So I might just relieve the back of the d bit, and whip a coarse thread down the body to get a bit of coolant down there, because a d bit, by defition has a air bit of area in contact with the bore. I’d probably take a gun drill and knock a coolant hole down the centre of the d bit and all.

 

Hence the enthusiasm for a boring tool after drilling to near size. 19mm gun drill and you are nearly there.

 

But then proper deep worm gun drills are not cheap. Especially not 19 mm ones!

 

One way to find out though!

Edited By mgj on 31/01/2011 23:18:01

[NilochParticipant @niloch]

mgj – welcome back!

[Ian S CParticipant @iansc]

it would’nt be too much trouble to drill a hole down the length of the D bit, so that coolant can be put down to the tip. I think a boring bar is the way to go. To square the end of the hole you need a bar with tool that is less than half the total diameter of the hole. Ian S C

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